Process for the production of flexible surface filter material for dealing with noxious substances

ABSTRACT

A process for the production of flexible surface filter material for dealing with noxious substances is described, in which a foam layer impregnated with a paste containing active particles is simultaneously joined to a preferably textile carrier layer and heavily compressed during the operation of joining it to the carrier layer. That produces a surface filter material which is highly suitable for use for protective clothing in particular because of its comparatively low level of thermal insulation, while the material is also distinguished in comparison with known materials by activity relative to noxious substances, which is uniform over the entire surface thereof.

The invention concerns a process for the production of flexible surfacefilter material for dealing with harmful gases or liquids (noxioussubstances), which has at least a first textile carrier layer and acompressed foam layer containing active particles, acting on the noxioussubstances, and joined to the carrier layer substantially over theentire surface area, wherein prior to the application of the carrierlayer the foam layer is impregnated with a paste containing the activeparticles in a binding agent and then compressed and adhesively joinedto the carrier layer.

The invention further concerns the production of surface materialsproduced in that way.

Several requirements frequently have to be fulfilled in the case ofsurface or flat filter materials. On the one hand the material is toexhibit adequate stability. If foam is used as the matrix for the filtermaterial, that stability will normally only be achieved if the foammatrix which carries the usually adsorbent particles is joined to alayer which is stable in respect of shape, substantially over the entiresurface area thereof. In addition there are a large number of areas ofuse, in particular for protective clothing, where it is desirable forthe surface or flat filter material to be of the smallest possiblethickness, in particular because such a material is better air-permeableand in particular more flexible, in comparison with thicker material.When using excessively thin foam however there is now the risk that theadsorption capacity falls sharply and the surface filter material nolonger has the protective effect which is required for the intended areaof use.

EP 0 526 264 Al already discloses a material for NBC-protectiveclothing, which as an inner layer includes a laminate comprising a foamlayer impregnated with a paste having activated carbon particles, and atextile carrier layer. In order to reduce thickness and improveair-permeability, it is proposed here that the foam layer is compressedsubsequently to the operation of impregnation with the paste containingthe activated carbon particles, and is adhesively joined to the carrierlayer over the entire surface area. In that respect, in accordance withthe state of the art, the procedure is such that compression of the foamlayer which is impregnated with the activated carbon paste is effectedbefore the foam layer is glued to the carrier layer. That proceduresuffers from a number of deficiencies, in which respect in particularthe lack of mechanical stability of relatively thin foam layers is to betaken into account. That has the result that the foam layer generallydistorts in the compression operation so that it can only be joineduniformly and over the entire surface area to the corresponding carrierlayer, with the greatest of difficulties. A further problem inprocessing thin foams is that they are highly liable to tearing. Anaspect which causes particular problems with the known process howeveris the point that, because of its low degree of stability, the foam iscompressed to different degrees under some circumstances, which meansthat the protective material has different protective effects atdifferent locations.

U.S. Pat. No. 4,787,949 discloses filters with a high degree of waterabsorption capability. Those filters comprise a filter paper layer. Apowder which is greatly water-absorbent is applied to the filter paperlayer. The powder layer is then covered with a thin fleece paper. Wateris then sprayed on to the thin fleece layer, whereby the water absorbentpowder becomes sticky and forms a certain join as between the filterpaper and the fleece layer. After water has been sprayed on, the entirearrangement is then compressed to reduce the thickness of the filterpaper layer.

The production of those known filters presupposes that the filter paperlayer can be compressed without problems and after compression remainsin the corresponding condition but does not return to the originalthickness by virtue of its elasticity because in fact the powder layerwhich serves to join the paper layer to the fleece layer only acts onthe filter paper layer, at the surface thereof. If the known processwere transferred to a surface filter material which has a foam layer asthe layer to be compressed, it would not be possible to achieve reliablecompression of the foam because the foam would repeatedly return to itsoriginal condition, because of its elasticity. In addition theabove-discussed problems relating to the absence of mechanical stabilityof the foam layer and the different degrees of compression of the foamlayer would not be eliminated.

Therefore the object of the present invention is to propose a processfor the production of flexible surface filter material, in which theoverall thickness is considerably reduced by compression of the foamlayer, but in which nonetheless the above-discussed disadvantages of thestate of the art do not arise, that is to say in particular there is nodanger of the surface filter material exhibiting different protectionproperties over its width, or the join between the foam and the carrierlayer not being uniform.

To attain that object, in a process of the kind referred to in theopening part of this specification, it is now proposed that theprocedure is such that the foam layer is impregnated with a paste whosebinding agent is--firstly only--dried and--only then--cross-linked athigher temperature, that firstly only the paste is dried, and that thenthe foam layer is simultaneously compressed and joined to the carrierlayer, wherein during the compression of the foam layer heating of thepaste is effected at least to the cross-linking temperature thereofduring a time which is sufficient for fixing of the foam layer by meansof the paste.

The combination according to the invention of the two workingoperations, namely compression of the foam layer on the one hand andjoining of the foam layer to the carrier layer on the other handprovides in a very simple manner that the low stability of the foamlayer is compensated. As a result of simultaneous joining to the carrierlayer during the compression step, that procedure ensures that the foamlayer is admittedly compressed in the desired manner, but at the sametime cannot stretch or distort uncontrolledly at other locations so thatthis provides a clean and tidy join to the carrier layer over the entiresurface and in addition the degree of the reduction in thickness of thefoam layer is the same over the entire surface area thereof, whichhowever means that the effectiveness in relation to noxious substancesis substantially equal over the entire surface area of the materialproduced in accordance with the invention, if the foam were onlyuniformly impregnated with the paste containing the active particles,prior to the compression step and joining of the foam to the carrierlayer.

The procedure in accordance with the invention also has in particularthe advantage that the foam is simultaneously fixed in the compressedcondition by virtue of cross-linking of the paste at the highertemperature. As cross-linking occurs, there is no fear that compressionof the foam would be lost again, for example in the event of highertemperatures subsequently having an influence thereon.

It has been found desirable if a belt calander is used for compressionof the foam layer and for joining same to the carrier layer. Such a beltcalander has the advantage that the laminate of foam and carrier layerremains in the gap for a comparatively long period of time and is thusheld under a suitable pressure, thereby reliably ensuring thatcross-linking of the binding agent of the paste takes place.

In general, the procedure will involve the use of a paste which containsparticles which act reactively and/or adsorbently in relation to thenoxious substances, in which respect preferably the particles with theadsorbent action are activated carbon particles, desirably in the formof powder carbon with a particle size of less than 50 μm.

Suitable binding agents for the paste are easy to find, on the basis ofthe above-discussed purpose and mode of operation. Good results can beachieved if the binding agent used in the paste are mixed polymers basedon acrylic acid esters which dry at temperatures of 100° to 110° C. andwhich completely cross-link at temperatures of 120° to 170° C.

For certain areas of use, surface or flat filter materials are required,in which the foam is covered on both sides. In accordance with theinvention, to produce such materials, the procedure involved isdesirably such that a further preferably textile cover layer is appliedsimultaneously with the first textile carrier layer to the surface ofthe foam layer, which is opposite the first textile carrier layer.Laminates which are produced in that way are also distinguished byaffording very good accuracy in respect of shape, flatness anduniformity in regard to adsorption capability over the surface areainvolved.

The connection of the carrier layer and optionally the cover layer tothe foam layer is advantageously made by means of a melt or fusionadhesion in the form of a coating, possibly over part of the surfacearea, on the carrier layer and/or cover layer and/or in the form of amesh introduced between the layers. The use of an adhesive mesh has inparticular the advantage that there is no need of a further workingoperation for applying adhesive to one of the layers of the laminate.

Finally it is in accordance with the invention that the binding agent ofthe paste with which the foam layer is impregnated serves for joiningthe foam layer to the carrier layer and optionally the cover layer. Aprocedure of that kind is only possible however if quite specificbinding agents are used which, although sufficiently sticky, nonethelessdo not close off the pores of the particles in the paste.

Flexible surface filter materials according to the invention can beenvisaged for a large number of areas of use which involve eitheradsorbing noxious substances or rendering them harmless by reaction withthe particles in the paste with which the foam is impregnated. However,a material produced by the process according to the invention can beparticularly desirably used for protective clothing, more specificallyfor the reason that it is comparatively thin and for that reasonprotective clothing produced from the material is far superior in regardto its characteristics regarding being worn by a person, than protectiveclothing comprising the previously known, comparatively thick materials.

To sum up the following can be emphasised:

With a procedure in accordance with the invention, what is obtained is avery thin flat or surface filter material with a particularly low levelof thermal insulation so that in particular protective clothing madefrom that material has a high degree of comfort in terms of wearing it,as on the one hand it acts very much like a textile material, it haslittle effect of making the wearer look bigger, and thus does not impedethe wearer in terms of freedom of movement, while on the other hand thethermal loading when wearing the suit is only very slight.

A particular advantage of the process according to the invention is thatthe operation of compressing the foam causes overlapping of theindividual foam sail portions, which results in deflection of the gaseswhich are charged with noxious substances. That provides that, in spiteof the considerable reduction in the thickness of material, theprotective effect achieved is not reduced, if not even improved, becausethe gas flowing through the filter material is correspondingly deflectedand changed in direction and consequently has to cover a comparativelylong path through the material.

As already discussed, simultaneous compression of the foam matrix andthe joining thereof to the carrier layer results in a high degree ofstability of the surface filter material, while in particular a uniformthickness of the layer of compressed foam and satisfactory joiningthereof to the carrier layer is achieved. As a result of cross-linkingof the binding agent of the paste, during the compression operation,satisfactory fixing of the layer which is very thin after thecompression operation is achieved.

In dependence on the various layers of the laminate, it is possible toproduce a large number of different products which are particularlysuited to the desired purpose of use. The carrier layer used may be forexample woven fabrics, knitted materials, non-woven materials or foils.It is also possible for the laminate to be provided with a coating whichis water-impermeable but water vapor-permeable.

The process according to the invention will be described hereinafter bymeans of an example.

EXAMPLE

A reticulated PU-foam of about 2 mm in thickness is impregnated in asizing apparatus with an activated carbon paste. The paste may alsoadditionally contain particles which reactively co-operate with thenoxious substances for removing them or for rendering them harmless, orit may even contain only such particles.

A paste in which a mixed polymer based on acrylic acid esters isemployed as the binder system is used as the activated carbon paste. Theactivated carbon used in the paste is a powder carbon with a particlediameter of less than 50 μm.

The binding agent of the paste is so selected and is of such acomposition that it dries in a range of 100° to 110° C. but onlycompletely cross-links in a range of 120° to 160° C.

After impregnation in the sizing apparatus the foam is dried at atemperature of 110° C. but not cross-linked.

The foam which has now been dried and impregnated is then fedsimultaneously with the carrier layer, for example a textile fabric orknitted material or also a fleece, to a belt calander where the laminateis exposed to a temperature of about 160° C. That results incross-linking of the binding agent of the activated carbon paste. In thebelt calander the foam is compressed to a thickness of only about 0.65mm (that is to say to about one-third of its initial thickness) under asuitably high pressure, for example about 220 bars, prior to completecross-linking of the binding agent.

A surface filter material produced using the above-described process isdistinguished by a satisfactory join between the carrier layer and thefoam. In addition, because of its small thickness and consequently itsrelatively low level of thermal insulation, it is highly suitable forprocessing in the form of protective clothing, in which respect thelaminate of textile carrier layer and compressed impregnated foam layercan be used for example only as an inner layer and a suitablymechanically stable outer layer is additionally provided.

To facilitate the processing operation or for certain areas of usehowever, in the working operation which is provided for compressing thefoam and for joining it to the carrier layer, that is to say on passingthrough the belt calander, a covering can be simultaneously applied tothe compressed foam, on the side opposite to the carrier layer, in whichcase a particular adhesive, for example a hot-melt adhesive, isdesirably used for fixing the cover layer in position. The hot-meltadhesive may for example be previously applied to the cover layer on oneside in a suitable process. However a particularly desirable procedureprovides that an adhesive mesh which passes into the belt calanderbetween the cover layer and the laminate serves for fixing the coverlayer on the carrier layer/foam laminate.

I claim:
 1. A process for producing a flexible surface filter materialfor dealing with harmful gases or liquids and other noxious substances,which comprisessimultaneously joining and compressing a foam layer thatcontains a dried paste of active particles in a non-crosslinked bindingagent to a textile carrier layer, under heat effective to cross-link thepaste for a time sufficient to fix the foam layer in its compressedstate by means of the paste, wherein the active particles act on thenoxious substances, and the binding agent has a cross-linkingtemperature higher than its drying temperature.
 2. A process accordingto claim 1, wherein the active particles are particles of activatedcarbon.
 3. A process according to claim 2, wherein the particles ofactivated carbon have a particle size less than 50 μm.
 4. A processaccording to claim 1, wherein the binding agent is mixed polymers ofacrylic acid esters, which dry at a temperature of 100° to 110° C. andcross-link at a temperature of 120° to 170° C.
 5. A process according toclaim 1, which further comprises simultaneously applying a cover layerto the surface of the foam layer that is opposite the carrier layer. 6.A process according to claim 5, wherein said cover layer is a textilelayer.
 7. A process for the production of flexible surface filtermaterial for dealing with harmful gases or liquids (noxious substances),which has at least a first textile carrier layer and a second compressedfoam layer containing active particles, acting on the noxioussubstances, and joined to the carrier layer substantially over theentire surface area, wherein prior to the application of the carrierlayer the foam layer is impregnated with a paste containing the activeparticles in a binding agent and then compressed and adhesively joinedto the carrier layer, characterised in that the foam layer isimpregnated with a paste whose binding agent dries and cross-links athigher temperature, that firstly only the paste is dried, and that thenthe foam layer is simultaneously compressed and joined to the carrierlayer, wherein during compression of the foam layer and joining thereofto the textile carrier layer, heating of the paste is effected at leastto the cross-linking temperature thereof during a time which issufficient for fixing of the foam layer by means of the paste.
 8. Aprocess as set forth in claim 7 characterised in that a belt calander isused for compression of the foam layer and joining thereof to thecarrier layer.
 9. A process as set forth in claim 7 characterized inthat a paste which contains particles which have an adsorbent and/orreactive action is used.
 10. A process as set forth in claim 9characterised in that activated carbon particles are used as theadsorbently acting particles.
 11. A process as set forth in claim 10characterised in that the paste contains powder carbon with a particlesize of <50 μm as active particles.
 12. A process as set forth in claim7 characterized in that mixed polymers based on acrylic acid esters,which dry at temperatures of 100° to 110° C. and completely cross-linkat temperatures of 120° to 170° C., are used as binding agent in thepaste.
 13. A process as set forth in claim 7 characterized in thatsimultaneously with the first textile carrier layer a cover layer isapplied to the surface of the foam layer which is opposite the carrierlayer.
 14. A process as set forth in claim 13 characterised in that thecover layer is a textile cover layer.
 15. A process as set forth inclaim 13 characterised in that a melt adhesive in the form of a coatingon the cover layer and/or in the form of a mesh introduced between thelayers serves for joining the cover layer to the foam layer.
 16. Aprocess as set forth in claim 13 characterised in that the binding agentof the paste with which the foam layer is impregnated serves for joiningthe foam layer to the cover layer.
 17. A process as set forth in claim 7characterized in that a melt adhesive in the form of a coating on thecarrier layer and/or in the form of a mesh introduced between the layersserves for joining the carrier layer to the foam layer.
 18. A process asset forth in claim 7 characterized in that the binding agent of thepaste with which the foam layer is impregnated serves for joining thefoam layer to the carrier layer.